The structure of multisubunit enzymes are being determined by methods of single crystal x-ray diffraction. The main enzymes being studied are glutamine synthetase from E. coli, and ribulose bisphosphate carboxylase-oxygenase (RuBisCO) from tobacco. A new preparative procedure has been devised for glutamine synthetase which frees it from the persistent contaminant, pgroE. X-ray grade crystals are being sought, and used for collection of x-ray diffraction data. The structure of RuBisCO at 4 A resolution is being solved, with the goal of determining the surface topology of the molecule.